Conducting chemical reactions in alkaline media



i without decomposition.

Patented Jan. 1, 1935 i l .1Q9sa194" v CONDUCTING CHEMICAL REACTIONS IN"ALKALINE'MEDIAV'V' 1 John J. Gr'ebeflana John H. Rant, Midland, Mich'.,assignors to The Dow Chemical Company, MidlamLt Mich, a corporation ofMichigan No Drawing. Application March 6, 1930,

Serial No. 433,807. '2 Claims. -(Cl. 260-154);

ing chemical reactions in alkaline media at elevatedtemperatures andpressures, and has for a particular object the preventionof stoppagestherein of a scale or incrustation ofcrystallized products such asmagnetic iron oxide. Other objects will appear as the descriptionproceeds.

An example of an organic chemical reaction of the aforesaid character isfound in the well? known process for the manufacture of a phenol byhydrolyzing a'halogenated aromatic hydrocarbon wherein the latter isheated under pres-- sure with an aqueous caustic alkali solution.

"When chlorobenzene and caustic soda aregemployed for the specificreactants the reaction, is

carried out at a temperature between about 300- and 400 C., preferablybetween 3.50? and 390 C.

On account of the high pressure developed at] the reacting temperature,between 3000 and.

5000 pounds per square inch, the process is most advantageously carriedout in a tubular type of autoclave comprising steel pipe coils.Thecaustic V alkali solution at the high temperature to which it isheated attacks the steel coils and dissolves iron from the exposedsurfaces thereof. When the reaction mixture is cooled down prior to dis:

charge from the tubular system, the dissolved M 7 iron is precipitatedout as magnetic iron oxide, F9304. This oxide forms as a hard, coherentscale or incrustation which builds up in the tubes, causing obstructionand eventual stoppage. This latter circumstance greatly shortens, 'theuseful life of the tubes, necessitating fre-; quent repairs andrenewals, and-also .gives rise to the dangerof blowouts wheneverstQPDage occur s.

'We have of a colloidal material, such as soap, which is capable ofwithstanding the reaction conditions I r I U The invention, then,consists of the method hereinafter fully described and particularlypointed out in the claims, the following description setting forth but afew of the various ways in which the principle of the invention may bepracticed. I

Under actual operating conditions for the manufacture of phenol by theforegoing process as found in plant practice, the tubular systemconsists of three sections or, zones, the first being the preheatingzone, the second the reacting zone This invention relates to methods forconduct; 1

ing zone the mixture of caustic soda solution IIQW'1fOl1I1d. that, thebuilding up of the aforesaid incrustation of magnetic ironoxide may besubstantially completely prevented; by adding to the reaction mixture;;a-, small amount and the third the cooling zone. In the preheati andchlorobenzene is, heatedupto about 350? C. whereat the reaction proceedsata: suitable rate.

In this zone the alkali solution attacks the iron 5 surface-exposedthereto and dissolves off some i of the iron until the. solution becomessaturated therewith. Due to such continuous attack and been reduced tothelimit of saftey. .By utilizing j certain corrosion-resistant alloysteels, however, a -lon'ger life for the tubes .may be attained. Withinthe reaction zone the attack upon the steel-tubes almost ceases, owingto the solution having become substantially saturated with re-- spectto-the iron compound before arriving inthe latter-zone. Toward the endof the zone,"how-- ever, where the temperature begins to drop, there isa tendency for some of the dissolved iron compound .to be precipitatedout and deposited upon the tube walls as a hard; adherent scale ofmagneticiron oxide, which gradually buildsup and constricts the'bore ofthetube until its use must. be discontinued in order to avoid dangerofcomplete stoppage. vIt has been found that the tubes may beIused about1000 hours in the lasthalf of the reaction zone before the conditionjust mentioned becomes such that replacement may be necessary. In thecooling zone, however, where the temperature of the hot, mixture isreduced from about 350 to? as low as 100 C. the deposition of ironoxide. scale occurs much more rapidly, at times necessitatingreplacement of the tubes. after as little as about 200 hours use. The.scale may be removed more or less completely from used tubes byrsuitabletreatment, but this involves disassembling the aparatus and considerableexpense is incurred in the handling. The tubes likewise deterioraterapidly under such treatment, 'and can safely be refitted for serviceonly .two-or three times, after which theymust be discarded; Thenecessity for frequentirew placement and renewal of tubes places a heavyburden of expense upon the process.

We have now found that the deposition of magnetic iron oxide scale inthe tubes in the reacting and cooling zones may be substantiallyprevented by introducing into the reaction mixture a colloidal substancestable under the conditions existing in the process, which has theeffect of inhibiting i grain growth of the precipitated iron oxide. Theaction of the colloid may consist simply in interv posing a film betweenthe individual particles of precipitated iron oxide which prevents theircohesion or agglomeration into larger masses and the building up into ahard scale, or the colloid may serve as a dispersing or defiocculatingagent to reduce the size of particles and prevent their coalescence. Theresult in either case is that the black iron oxide is precipitated in ahighly dispersed form which is carried along by the stream of liquid inthe tubes and is discharged from the apparatus admixed with the reactionproduct.

As a suitable colloid for introducing with the reaction mixture we havefound soap to :be particularly effective, although other colloids andpeptizers such as sodium tartrate, chromic oxide, saponin, tannin,glycerine or glucose, have also or vegetable fats, the alkali salts ofthefatty acids, such as sodium oleate or sodium stearate,

with equal advantage. The .amount of soap or other colloid to be addedis about 0.025 to 0.1 per cent of the solids present, althoughsomewhatmore or less may be employed without materially changing the result- Itis sufficient to provide" enough of the soapto mix with-the precipitatedblack iron oxide and prevent crystal growth','and.

in practice the amount above mentioned has been found ample;

without affecting the action of the soap.

.When'strong alkali'solutions, i.'e. about 30 to 40 per cent;, areemployed,-however, there is an added advantage from using the soap;sincef at tinctly claim as ourinventiomsuch concentration some of thesalt formed in the reaction is crystallized out and the crystals havebeen found to exert a scouring or eroding action on the tubes due to thehigh velocity of flowthferein. .In the presence of soap or similarcolloid, however, crystal growth is impeded or inhibited just as withthemagnetic iron oxide, the size of the precipitated particles is keptsmall and a.

crystal sludge of soft consistency is formedwhich does not abrade thetube walls as greatly as the,

larger crystals otherwise formed. By means of the improved procedurehereinbefore described it is possible substantiallyto pre-- vent scalingand incrustation of the tubesin' the reacting and cooling zones sothattheir'life is increased almost indefinitely. The'savings' there byeffected are of material consequence in a commercial process, since notonly is the frequent renewal of tubes largely eliminated but also delaysany interruption of process incident thereto. 1

The separation of the magnetic iron oxide sludge'from the reactionproduct maybe carried out by usual means, such as filtration, orbydistilling off volatile products whereupon the sludge remains in thestill residue. V

While our invention has been described illustratively by reference to,the manufacture of phenol by reacting chlorobenzene and an aqueousThecon'centration of the caustic 1 alkali solution may be'varied withinwide limits steps stated by any of the following claims or the causticsoda solution, it is broadly applicable to similar processes for themanufacture of phenolic compounds by reaction of a hydrolyzablesubstituted derivative of an aromatic hydrocarbon, e. g. a halogenatedor sulphonate d aromatic hydrocarbon, and an aqueous caustic alkalisolution at an elevatedtemperature and pressure. The invention stillfurther is adapted for use in any chemical process wherein an aqueouscaustic alkali solution is heated under pressure in a tubular or otherform of autoclave. While greater advantage attaches to the use thereofin operationscarried out in tubular apparatus, due to the greaterreadiness with which passages of relatively small bore may be obstructedor stopped up completely, there is also advantage when used withothertypes of pressure apparatus, the operation of which may be deleteriouslyaffected by the accumulation on the Walls thereof of a hard,

equivalent of such stated step or steps be employed. 4 i

We therefore particularly point out and dis- ;1. In a method ofpreparing phenol by heating underpressure at a temperature between 300and 400 C. in contact with surfaces of ferrous metal a reaction mixturecomprising chlorobenzeneand aqueous sodium hydroxide solution, the

improvement which consists in adding to the.

said reaction'mixture a relatively small amount of a soap, whereby topreventthe'formation on thew'alls of" the reaction vessel of a hardadherent scale of magnetic iron oxide formed by chemical action betweenthe aqueous alkali and the iron container for the said reactionmixture."

2. Ina method of preparing phenol by heating under pressure at atemperature of between 300 'and400" C.in contact with surfaces offerrous metal a reaction mixture'comprising chlorobenzene-and, aqueoussodium hydroxide solution, the improvement which consists in adding tothe said I reaction mixture up to 0.1 per cent of a soap,

whereby to prevent the formation on the walls or the reaction vessel ofa hard adherent scale of magnetic'iron oxide formed by chemical actionbetweenthe aqueous caustic alkali and the iron containerfor the saidreaction mixture.

. JOHN J. GREBE.

- JOHN H. REILLY.

